1. Field of the Invention
The present invention relates to a projector that projects an arbitrary image on a screen, and in particular, to a projector comprising an automatic vertical and horizontal keystone correction function for a projected image which is based on a phase difference sensor system, a range finding method used for the projector, and a recording medium on which the range finding method is recorded.
2. Description of the Related Art
With a projector that projects an arbitrary image on a screen, a range finding pattern image is normally used to measure the distance from the projector to the screen. A point at which the contrast of the pattern image changes (normally a white part) is set as a measurement point. A phase difference sensor senses phase differences of reflected lights reflected from the measurement point to calculate the distance (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-204495).
There are at least three measurement points in the pattern image. Range finding is executed on these measurement points to detect the slope angle of a projection surface of the screen. Then, the distortion of an image projected on the screen corresponding to the slope angle is corrected.
The correction of distortion of the projected image is called “keystone correction” because the distortion is shaped like a keystone.
The range finding pattern image is dedicated for range finding. The range finding pattern image is typically composed of a simple light-dark pattern such as a black-and-white mark pattern which can be easily sensed by the phase difference sensor. Thus, the pattern image does not appear attractive when projected on the screen. Further, the pattern image itself does not convey any message. Accordingly, the pattern image remains a nuisance for a user watching the projected image until the range finding is finished.